Method for optical bleaching coated papers



' 3,047,390 METHOD FOR OPTECAL BLEACHING COATED PAPERS Willem KarelKoerber and Ferdinand Leonard Schouteden, Wilrijk-Antwerp, Belgium,assignors to Gevaert Photo-Prodncten N.V., Mortsel, Belgium, a companyof Belgium No Drawing. Filed June 2, 1958, Ser. No. 739,211 Claimspriority, application Netherlands June 6, 1957 9 Claims. (Cl. 96-82) Thepresent invention relates to a process for whitening the surface colorof papers provided with one or more surface coatings the composingelements of which are not able to strongly bind optical bleachingagents, and more particularly relates to a process for brightening thewhite areas in photographic images whereby the wandering of opticalbleaching agents out of the photographic layers is inhibited.

It is generally known that the reflecting power of the paper surface canconsiderably be increased by applying a surface coating containingfilling substances with a high degree of whiteness. Examples of suchfilling substances are i.a. titanous dioxide, barium sulphate, zincsulphide, calcium carbonate and silicium dioxide. In this way, thesurface color of the paper can be whitened to a certain extent, but notcompletely. If, however, a paper is concerned where this surface coatingcontains besides the white pigments products which are slightly coloredor which are colored during the further treatments or during the storageof the paper or where on this surface coating still one or more otherlayers are coated which contain such products, the brightening eifectobtained by applying the reflecting surface coating is nullified whollyor partially. Thus it is seen for instance that when a baryta-coatedpaper support is coated with a photographic emulsion, the surface colorof the photographic paper is not completely white so that even thewhitest areas in a photographic image obtained upon such a support stillabsorb a considerable amount of light. This coloration depends onvarious factors such as the reflecting power of the used paper, thequality of the gelatin applied as binding agent for the photographiclayers and the kind and the amount of compounds such as e.g. sensitizingdyestuffs added to the photographic layers during the manufacture of thelight-sensitive element. This coloration can also be caused by coloreddecomposition products which are formed during the development andfurther treatments of the photographic element in the photographiclayers or are absorbed by these layers from the baths wherein they wereformed. Since the cellulose fibers wherefrom the paper is composed, aswell as the gelatin used as binding agent for the photographic layersand the decomposition products which are formed during the processingabsorb the light particularly in the range of the short wave-lengths,the photographic paper shows in most cases a slight yellow tinge.

It has been proposed to eliminate this defect by adding to the papersupport, to a surface coating and/or to another superposed layer,dyestuffs or pigments which absorb in the range of the longwave-lengths, so that the spectral partition of the reflected visiblelight is equal to that of the incident visible light and the paper showsa neutral tone. Thus, it is known to add organic light-fast bluedyestuffs to a baryta-coating which is applied to a paper supportdestined for receiving a photographic emulsion layer.

By application of this process, the incident visible light is notcompletely reflected but partly absorbed by the yellow paper and partlyby the blue dyestuif or the blue pigment. Even in the most favorablecases where only an extremely small amount of dyestufi or pigment isretii quired, such as for instance for the manufacture of a photographicpaper starting from a baryta-coated paper of good quality, from a littlecolored gelatin and from sensitizing dyestuffs which during theprocessing can easily be removed from the photographic layers, thewhitest areas in the photographic image will not completely reflect thevisible light.

According to a more recent process, substantially colorlessblue-fiuorescing ultraviolet-absorbing compounds are added during themanufacture to the paper or to one or more surface coatings e.g.compounds absorbing ultraviolet radiation of between about 3000 Angstromunits and 4000 Angstrom units and emitting fluorescent light of betweenabout 4000 Angstrom units and 5500 Angstrom units. These compounds canbe added during the manufacture of a photographic paper for instance tothe paper support, to the layer wherein the photographic image is formed(for instance the silver halide emulsion layer) or to a layertherebetween (for instance a baryta-coating). The photographic elementcan also be treated with a solution of such compounds during theprocessing.

The spectral partition of the reflected visible light is equalized bythe use of these optical bleaching agents to that of the incidentvisible light by conversion of a part of the incident ultra-violet raysto which the human eye is not sensitive into the blue light absorbed bythe paper. The reflected light is now completely neutral, without lossof a part of the visible incident light. By applying this method in themanufacture of photographic paper, it is not only possible to obtain aneutral image tone together with a strong reflecting power of the whiteareas in the photographic image, but moreover photographic images to beviewed by reflection can be manufactured which reflect more visiblelight than they properly receive, i.e. when an excess of opticalbleaching agent is used so that more ultra-violet light is convertedinto blue light than is necessary to correct the yellowness of thephotographic paper. In this way, it is possible to change the image-toneto a colder, i.e. a more bluish tone.

In connection with the above described process, according to which anoptical bleaching agent is added to the paper itself and/or to thebaryta-coating and/ or to the emulsion layer, it is to be noted that bythe addition of the optical bleaching agent to the paper alone, nosuflicient brightening of the images is obtained, since the whiteningeffect is annulated for a great part by the superposed baryta-coatingwhich is present in most of the photographic papers.

It is evident that the practical result, which can be attained whenapplying the above-mentioned process, fully depends on the amount ofoptical bleaching agent which is still present in the completelyfinished paper. Consequently, it has been tried to prevent that theoptical bleaching agents should be removed wholly or partially from thelayers of the photographic element for instance when treating thephotographic elements in the usual treating baths.

None of the different propositions to counteract the wandering of theoptical bleaching agents out of the emulsion and/or the baryta-coatinghas hitherto been found effective in this respect.

Summarizing, the great difficulty in finding an effective solution forthis problem mainly results from the fact that the optical bleachingagents are not or at least insufficiently adsorbed on elements, such asgelatin and baryt-a of which the usual surface-coatings applied to thepaper are composed.

It is therefore an object of the present invention to provide a methodfor increasing the whiteness of the surface of a paper provided with atleast one surface coating whereby the wandering of the optical bleachingagents out of the layers wherein they were incorporated is inhibited.

It is a further object of the present invention to provide a method forincreasing the whiteness of photographic papers. Still further objectswill appear in the following description and examples.

It has now been found that the wandering of optical bleaching agents outof the layers in which they were incorporated can be inhibitedcompletely by treating finely divided water-insoluble macromolecularproducts with a solution or a dispersion of an optical bleaching agentwhich possesses a pronounced substantivity to the macromolecular productused and by adding the fluorescing mass obtained to one or more surfacecoatings. Thus, in the manufacture of a photographic paper thefluorescing mass can be incorporated into a layer between thepaper-support and the layer wherein the photographic image is formed orinto the latter layer itself. Macromolecular products which in finelydivided state are suitable for carrying out the method according to thepresent invention, are i.a.: cellulose, polyesters, polyamides andureaformaldehyde resins. As distinct from the generally adoptedtendency, 2

which consists in using polymers with high degree of polymerization formost of the applications, those polymers having a low degree ofpolymerization are to be preferred among the synthetic polymers forcarrying out the process according to the present invention sincecontrary to the high polymeric products they can be divided very finelyand in this way can bind relatively more bleaching agent.

Suitable polyesters for carrying out the process according to thepresent invention are for instance the oligomers of aromatic polyesterswhich can be prepared in a simple way by re-esterifying the dimethylester of an aromatic acid with a lower diol in the presence of acatalyst which mainly influences the re-esterification and to a lessextent the polycondensation. For further elucidation, we givehereinafter some examples relating to the preparation of some oligomersof the polyester type which can be applied for carrying out the processaccording to the present invention.

PREPARATION 1 100 g. of dimethylterephthalate, 75 cm. of ethyleneglycol(molar proportion 112.63) and 0.015 g. of zinc acetate are heated for 3hours in such a way that the liberated methanol (about 40 cm. is slowlydistilled over. When no methanol distills over anymore, temperature israised to 180190 C. and slowly increased until about 30 cm. of glycolhas distilled over. The reaction mixture is crushed after cooling and asthe case may be, ground under the addition of a certain amount of Water.

PREPARATION 2 100 g. of a mixture consisting of equal parts of isoandterephthalic acid dimethylester, 75 cm. of glycol and 0.030 g. of zincmonomethyl terephthalate are heated for 3 hours so that the liberatedmethanol slowly distills over. When no methanol distills over anymore,the temperature is raised to 180-l90 C. and slowly increased until 38cm. of glycol has distilled over. After cooling, the reaction mixture iscrushed and as the case may be, ground under addition of a certainamount of water.

PREPARATION 3 50 g. of dimethylisophthalate, 50 g. ofdimethyl-pcarboxyphenyl-sulphone, 60 cm. of glycol and 0.020 g. of zincacetate are heated for 3 hours, so that the liberated methanol distillsover slowly. When no methanol distills over anymore, the temperature israised to 200 C. and maintained until about 30 cm. of glycol hasdistilled over. After cooling, the reaction mixture is crushed and asthe case may be, ground under addition of a certain amount of water.

A polyamide which is suitable for carrying out the method according tothe present invention can be prepared as follows:

PREPARATION 4 20 g. of caprolactam and 0.05 g. of carbonate-free sodiumhydroxide are heated for about minutes at 95 C. whilst pure nitrogen isbubbled through. Thereafter, heating is continued for another minutes at230 C. and then the reaction mixture whilst strongly stirring is pouredout into 1 /2 1. of water, sucked off and thoroughly washed with warmwater.

Suitable optical bleaching agents for carrying out the process of thepresent invention are described i.a. in Phot. Korrespondenz, 94 (1958),p. 5.

For carrying out the process according to the present invention, acertain amount of the finely divided macromolecular product is dispersedin water. To this suspension is added a solution of the opticalbleaching agent involved. If the optical bleaching agent is not or notsufficiently soluble, it can be added in dispersed form to thesuspension. The treatment of the macromolecular product with the opticalbleaching agent is preferably carried out at a temperature between and100 C. and is continued until no more fluorescing substance is bound.After sucking off, a strongly fluorescing paste is thus obtained whichstrongly retains the fluorescing substance and v which can be added tothe coating composition which is to be applied to a paper support. Thusthe fluorescing mass can for instance be added to a baryta-compositionwhich is spread upon a paper whereon a photographic emulsion is to becoated. The fluorescing paste can, as the case may be, be incorporatedin a photographic emulsion itself, in which case very favorable resultscan be attained by using as macromolecular product an ureaformaldehyderesin such as described in the Belgian specification 451,470 and whichi.a. also compreses condensation products with a characteristically lowdegree of polymerization.

The wandering of the optical bleaching agent out of the layer, whereinit was applied, is practically completely excluded by applying themethod according to the present invention, so that the exposedphotographic element after complete processing, which even may comprisea protracted rinsing, yields a photographic image wherein the whiteareas are strongly brightened.

The method according to the present invention can be applied forbrightening the white areas in usual photographic black-and-White andcolored images as well as for whitening the surface color of any othersurfacecoated paper such as for instance papers on which a positivephotographic image is formed by applying the silver halide diffusiontransfer process, or papers on Which an image is printed by means of anhectographic process.

The present invention is further illustrated in the following exampleswithout limiting, however, the scope thereof. The formula of some of theoptical bleaching agents used in the examples, are shown in theaccompanying drawings.

Example I 1 kg. of the polyester paste, obtained according toPreparation 1 is dispersed in 1500 cm. of a 5% aqueous solution ofsodium sulphate together with 10 g. of a,,8-

di(S-methylbenzimidazyl-Z)-ethylene (cf. formula 1).

By strongly stirring, the whole mass is kept in suspension for 30minutes at a temperature of 80-90 C. After ,this treatment, thefluorescing mass is sucked off and the strongly fluorescing paste thusobtained is added to a baryta composition which is spread on a paper tobe coated with one or more photographic emulsion layers. The whitenessof the surface color of the photographic paper thus treated is not loston rinsing and the photographic element yields after exposure andcomplete finishing a photographic image wherein the white areas arequinoline (cf. Formula 2), or a,,8-di-(benzimidaZyl-2)- ethylene (cf.Formula 11).

Example 2 1 kg. of the polyester paste obtained according to Preparation2 is dispersed in 1500 cm. of water together with g. ofa,B-di(5-methylbenzimidazyl-2)ethylene (cf. Formula 1). By stronglystirring, the whole mass is kept in suspension for 30 minutes at atemperature of 60 C. After this treatment, the fluorescing mass issucked off and the strongly fluorescing paste thus obtained is added toa baryta composition which is spread on a paper. The surface color isclearly white and is not modified when the paper is rinsed with waterfor a longer time.

A similar result is attained when on carrying out the process of thepresent example, the a,[3-di(5-methylbenzimidazyl-2)-ethylene isreplaced by a same amount of 1,3 dioxo 2 butyl 6acetylamino-1,2,3l'l-benz de[isoquinoline] (cf. Formula 2) ora,fl-di(5-methylbenzoxazolyl-2)-ethylene (of. Formula 12).

Example 3 1 kg. of the polyester paste obtained according to preparation3 is dispersed in 1500 cm. of a 5% aqueous solution of sodium sulphatetogether with 10 g. of a,B-di(5- methylbenzimidazyl-Z)-ethylene (of.Formula 1). By strongly stirring, the whole mass is kept in suspensionfor 30 minutes at a temperature of 90 C. After this treatment thefiuorescing mass is sucked off and treated as indicated in Example 1.

A similar result is attained when on carrying out the process of thepresent example, the a,,8-di(5-methylbenzimidazyl-2)-ethylene (of.Formula 1) is replaced by a same quantity of1,3-dioxo-2-butyl-6-acetylamino-l,2,3H- benz [de]isoquinoline (cf.Formula 2), a,fl-di(benzirnidazyl-2)-ethylene (cf. Formula 11) ofa,,8-di(5-metl1ylbenzoxazoyl-2)-ethylene (cf. Formula 12).

Example 4 1 kg. of the polyamide paste obtained according to thePreparation 4 is suspended in 1500 cm. of a 5% aqueous solution ofsodium sulphate together with 10 g. of 4,4- bis(2 hydroxy4-phenylamino-1,3,5-triazyl-6)-diaminostilbene-2,2-disulphonic aciddisodium salt (cf. Formula 3). By strongly stirring the whole mass iskept in suspension for 30 minutes at a temperature of 8090 C. After thistreatment the fluorescing mass is sucked Off and treated as indicated inExample 1.

A similar result is attained when on carrying out the process of thepresent example, the 4,4'-bis(2-hydroxy-4- phenylarnino 1,3,5 triazyl6)-diaminostilbene-2,2- disulphonic acid disodium salt is replaced bythe same amount of a,,i-di(5-methylbenzimidazyl-2)-ethylene (cf.Formula 1) or a,B-di(S-methylbenzoxazolyl-Z)ethylene (cf. Formula 12).

Example 5 1 kg. ground cellulose is dispersed in 1000 cm. of water. Tothis suspension are added 400 cm. of a 1% aqueous solution of thecompound 4,4-bis(2-hydroxy-4-phenylamino 1,3,5 triazyl6)-diaminostilbene-2,2-disulphonic acid disodium salt (cf. Formula 3).By strongly stirring, the whole mass is kept in suspension at atemperature of 50100 C. until no more fluorescing substance is bound bythe cellulose. After this treatment the fluorescing mass is sucked offand the thus obtained strongly fluorescing paste is added to a barytacomposition which is spread upon a paper whereon one or morephotographic silver halide emulsion layers are to be coated. Thewhiteness of the surface color of the photographic paper thus treated isnot lost on rinsing and the photographic element yields after exposureand complete finishing a photographic image wherein the light parts arestrongly brightened.

A similar result is attained when in the execution of the process of thepresent example, the 4,4'-bis(2-hydroxy- 4 phenylamino 1,3,5triazyl6)-diaminostilbene-2,2- disulphonic acid disodium salt isreplaced by a same amount of 4,4 bis(2 amino 4-hydroxyethylamino- 1,3,5triazyl 6) diaminostilbene 2,2 disulphonic 1 acid disodium salt (cf.Formula 4), 4,4-diaminostilbene- Example 6 1 kg. of ground cellulose isdispersed in 1000 cm. of water. To this suspension are added 400 cm. ofa 1% ethanol solution of the compound 1,3-dioxo-2-butyl-6-acetylamino1,2,3H-benz[deJisoquinoline (cf. Formula 2). By stronglystirring, the whole mass is kept in suspension at a temperature of 50l00C. until no more fiuorescing substance is bound by the cellulose. Afterthis treatment, the fiuorescing mass is sucked OE and further treated asindicated in Example 5.

A similar result is attained when on carrying out the process of thepresent example, the 1,3-dioxo-2-butyl- 6-acetylarnino-1,2,3H-benz[de]isoquinoline is replaced by a same quantity of1,3-diphenyl-5(p-iodophenyl)-pyrazoline (Formula 9).

Example 7 1 kg. of ground cellulose is dispersed in 1000 cm. of water,together with 10 g. of a,,8-di(S-methylbenzimidazyl- 2)-ethylene (cf.Formula 1). By strongly stirring the whole mass is kept in suspensionfor 30 minutes at a temperature of 50100 C. After this treatment thefiuorescing mass is sucked off and further treated as given in Example2.

A similar result is attained when on carrying out the process of thepresent example, the a,fl-di(5-methylbenzimidazyl-2)-ethylene isreplaced by a same amount of a,18-di(benzimidazyl-2)-ethylene (of.Formula 11) or up di(5 methylbenZoxazolyl-2)-ethylene (cf. Formula 12).

Example 8 1 kg. of an ureaformaldehyde resin, prepared according to themethod indicated in Example 1 or 2 of the Belgian specification 451,470is dispersed in 3000 cm. of water together with 10 g. ofa,,B-di(5-methylbenz imidiaZyl-2)-ethylene (cf. Formula 1). By stronglystirring, the whole mass is kept in suspension for 30 minutes at atemperature of 5070 C. After this treatment, the fluorescing mass issucked off. 50 g. of the strongly fluorescing paste thus obtained areadded to 1 kg. of a photographic silver halide emulsion coated on apaper support. The whiteness of the surface color of the photographicpaper thus obtained is not lost on rinsing and the photographic elementyields after exposure and complete finishing a photographic imagewherein the white areas are strongly brightened.

Example 9 1 kg. of an ureaformaldehyde resin prepared according to themethod indicated in Example 1 or 2 of the Belgian specification 451,470is suspended in 3000 cm. of water. To this suspension are added 1000 cm.of a 1% ethanol solution of the compound 4,5-diphenylimidazolone-Z (cf.Formula 10). By strongly stirring, the whole mass is kept in suspensionfor 30 minutes at a temperature of 50-70 C. After this treatment, thefluorescing mass is sucked oif and further treated as indicated inExample 8.

The following is a list of the structural formulae of the opticalbleaching agents mentioned in the above examples, the numbers of thelist corresponding to those set forth 7 8 in parentheses following thename of the compound for ease of correlation: F (1) OCH=CH-O ml HT q/ lH H 11 0-- OH CH CH;

I l (1 H H *1 n (2 iflrcHrOHrOHg N/COH CHC\N/ 6 The preparation ofcompounds in the above list are described in the following citations,the initial once again corresponding to the numbers of the structuralformulae and examples:

(1) Chem. Abs., B 44 (1950), p. 2251. (2) US. patent specification No.2,600,080. NH OO OH3 (3) British patent specification 495,479, p. 3, N0.13; German patent specification 752,677, page 8; Danish (3) N patentspecification No. 63,688 (1945); German patent O 9 Q specification972,067.

| (4) British specification 624,051. SOBN, (5 F. Benber: Ber., 19(1886), page 3235.

o (6) Prepared analogously to Britsh specification No. 5 2 624,051.

(7) Id. (4) (8) Blancophor R trademark transferred from I. G.HOCHZGHZNHO/ o-NH H= I Farbenindustrie Aktiengesellschaft toFarbenfabriken II I Bayer A.G., Danish patent specification 63,688(1945),

die E-rzeugung Von Holtzstoif, Zellstofi, Papier und Pappej ChemischeTechnologie der Cellulose, 8. Iahrgang, Darmstadt, April 1954, Heft 7/8,A. E.

SOzNa German patent specification 972,067, Zeitschrift fiir i NH (5)Siegrist Die Anwendung optischer Aufhellmittel in der HN CH=OH NH G OPapiermdustrie, s. 114 115.

1 1 9 Neunhofer and Rosahl: Chem. Ber., 86 (1953); s.

1146. (6) (10) Org. Synth. Coll, vol. II, p. 231.

N We claim: H3C (CH2)3 0 (OHZ)3 NH O% O 1. Light-sensitive photographicpaper comprising a I H paper base, a white pigmented coating and alight-sensig tive silver halide emulsion layer, said White pigmented 0coating containing a fluorescent mass comprising a mem- HaC(CH1)a z)a1IH 2 her selected from the group consisting of a,,6-di(5-methyl- (7) OHCH N r 3 H C(l]OH (0-OII2-OH2)2-CHzNH-(] (flJ-NH- OH:

N CH3 CH1 N\ SOSH 2 5 1 i n o i-ong o t a ooHi-om)i-on n1\r CH3 CH3G-NEP-C ONI-IQCH=CH- NHC O-NHO SO Na SO3Na (9) benzirnidazyl-Z-ethylene, oc,fi-di (benzirnidazyl-Z -ethyl- Hfiflene,a,B-di(5-methylbenzoXaZolyl-2)-ethylene and 1,3- C idioxo-Z-butyl-6-acetylamino 1,2,3H benz [de] isoquinoline, and a finelydivided polyethyleneglycolphthalate.

N 2. A photographic paper as defined in claim 1, wherein the phthalateis the terephthalate.

3. A photographic paper as defined in claim 1, wherein the phthalate isisophthalate.

4. A photographic paper as defined in claim 1, wherein said polyethyleneglycolphthalate contains equal amounts (10) of the moities ofisophthalic acid and terephthalic acid.

I I 5. A photographic paper as defined in claim 1, wherein saidpolyethylene glycolphthalate contains equal amounts 0 of the moities ofisophthalic acid and p-car boxyphenyl- 0 sulphonic acid.

6. A photographic paper as defined in claim 1, wherein the fluorescentagent is a1pha,heta-di(5-methylhenzimid azyl-Z -ethy1ene.

7. A photographic paper as defined in claim 1, wherein the fluorescentagent is alpha,beta-di- (benzimidazy1-2)- 5 ethylene.

8. A photographic paper as defined in claim 1, wherein the fluorescentagent is alpl1a, beta-di(5-methy1 benzoXaz0lyl-2) -ethy1ene.

9. A photographic paper as defined in claim 1, wherein m the fluorescentagent is 1,3-dioxo-2-butyl-6-acetylamino- 1,2,3H-benz [de] isoquinoline.

References Cited in the file of this patent UNITED STATES PATENTS Libbyet a1. Nov. 8, 1955 FOREIGN PATENTS France Nov. 2, 1942 Holland Oct. 15,1946

1. LIGHT-SENSITIVE PHOTOGRAPHIC PAPER COMPRISING A PAPER BASE, A WHITEPIGMENTED COATING AND A LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER,SAID WHITE PIGMENTED COATING CONTAINING A FLUORESCENT MASS COMPRISING AMEMBER SELECTED FROM THE GROUP CONSISTING OFA,B-DI(5-METHYLBENZIMIDAZYL-2)-ETHYLENE,A,B-DI(BENZIMIDAZYL-2)-ETHYLENE, A,B-DI(5-METHYLBENZOXAZOLYL-2)-ETHYLENEAND 1,3DIOXO-2-BUTYL-6-ACETYLAMINO - 1,2,3H - BENZ (DE) ISOQUINOLINE,AND A FINELY DIVIDED POLYETHYLENEGLYCOLPHTHALATE.